Soda-lime-silica glass-ceramic

ABSTRACT

A soda-lime-silica glass-ceramic article having an amorphous matrix phase and a crystalline phase is disclosed along with a method of manufacturing a soda-lime-silica glass-ceramic article from a parent glass composition comprising 47-63 mol % SiO2, 15-22 mol % Na2O, and 18-36 mol % CaO. The crystalline phase of the glass-ceramic article has a higher concentration of sodium (Na) than that of the amorphous matrix phase.

The present disclosure is directed to glass-ceramics, and, morespecifically, to soda-lime-silica glass-ceramics.

BACKGROUND AND SUMMARY OF THE DISCLOSURE

Soda-lime-silica glass, also referred to as soda-lime glass, is commonlyused in the commercial production of hollow and flat glass articles,such as glass containers and windows, and is based on a Na₂O—CaO—SiO₂ternary system. Relatively small amounts of other oxides may be added toadjust the properties of the glass for various purposes. For example,aluminum oxide (Al₂O₃), or alumina, is usually included in commercialsoda-lime glass compositions to improve chemical resistance, regulateviscosity, and prevent devitrification of the glass. Commercialsoda-lime glass compositions generally comprise, by weight, 70-75%silica (SiO₂), 11-15% soda (Na₂O), 6-12% lime (CaO), and 0.1-3% alumina(Al₂O₃).

Glass is commercially produced by melting a mixture of solidglass-forming materials known as a glass batch in a melting tank of acontinuous glass furnace to produce a volume of molten glass known as amelt. Glass articles having a non-crystalline amorphous structure areproduced from the melt by cooling the molten glass along a temperatureprofile that is calculated to avoid nucleation and crystal growth withinthe glass. The unintentional and uncontrolled crystallization ordevitrification of soda-lime glass is generally considered to beundesirable because it typically results in the heterogeneous formationof relatively coarse crystals of varying size, which can reduce thetransparency and mechanical strength of the glass. Also, devitrificationof conventional soda-lime glass compositions is known to producedevitrite (Na₂O.3CaO.6SiO₂), wollastonite (CaO.SiO₂), and/or quartz,cristobalite or tridymite (SiO₂) crystals within the glass, whichreduces the chemical resistance of the residual glass phase byincreasing the Na₂O concentration therein.

Glass-ceramic materials, having a homogeneous distribution offine-grained crystals throughout a residual amorphous phase, may beformed by the controlled crystallization or ceramization of a parentglass. In particular, glass articles may be formed from a parent glasscomposition and then intentionally transformed into glass-ceramicarticles by heat treating the parent glass at a temperature above itsglass transition temperature (Tg) for a sufficient amount of time forbulk nucleation to occur within the glass, followed by crystal growth.The resulting glass-ceramic articles may exhibit certain desirable andimproved properties over that of the parent glass. For example,glass-ceramic articles may exhibit a higher viscosity vs. temperatureprofile and a lower coefficient of thermal expansion. In addition, thecrystal grains in the glass-ceramic articles may inhibit crackpropagation, which may result in increased strength.

A general object of the present disclosure, in accordance with oneaspect of the disclosure, is to provide a soda-lime-silica parent glasscomposition that can be used to produce soda-lime-silica glass-ceramicarticles having improved chemical resistance and fracture toughness, ascompared to conventional soda-lime-silica glass.

The present disclosure embodies a number of aspects that can beimplemented separately from or in combination with each other.

In accordance with one aspect of the disclosure, a body of asoda-lime-silica glass-ceramic container, which defines a shape of thecontainer, comprises a soda-lime-silica glass-ceramic having anamorphous matrix phase and a crystalline phase. An overall chemicalcomposition of the soda-lime-silica glass-ceramic comprises 47-63 mol %SiO₂, 15-22 mol % Na₂O, and 18-36 mol % CaO. The concentration of sodiumin the crystalline phase is greater than the concentration of sodium inthe amorphous matrix phase.

In accordance with another aspect of the disclosure, there is provided amethod of manufacturing a soda-lime-silica glass-ceramic container inwhich a glass body is initially formed from a parent glass compositionthat comprises 47-63 mol % SiO₂, 15-22 mol % Na₂O, and 18-36 mol % CaO.The glass body is in the shape of a container and is subjected to athermal treatment to promote bulk in situ crystallization of the glassbody such that the glass body is transformed into a glass-ceramic bodyhaving an amorphous matrix phase and a crystalline phase homogeneouslydispersed throughout the amorphous matrix phase.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure, together with additional objects, features, advantagesand aspects thereof, will be best understood from the followingdescription, the appended claims and the accompanying drawings, inwhich:

FIG. 1 is a side elevation of a soda-lime-silica glass-ceramic article,namely, a container;

FIG. 2 is a graphical illustration of a thermal treatment schedule formanufacturing a soda-lime-silica glass-ceramic container, in accordancewith one embodiment of the present disclosure;

FIG. 3 illustrates x-ray diffraction patterns of two stoichiometricNa₂O.2CaO.3SiO₂ glass-ceramic samples having different degrees ofcrystallization; and

FIG. 4 is a graphical plot of light transmission through samples ofconventional flint container glass, stoichiometric Na₂O.2CaO.3SiO₂glass, and partially and fully crystallized Na₂O.2CaO.3SiO₂glass-ceramics.

DETAILED DESCRIPTION

Soda-lime-silica glass-ceramic articles—having a crystalline phase andan amorphous matrix phase—can be produced from a parent glasscomposition that is formulated to approximate a stoichiometric1Na₂O.2CaO.3SiO₂ system, and thus may be referred to as NC₂S₃ glass.Conventional soda-lime-silica glass compositions, on the other hand, aretypically based upon a stoichiometric 1Na₂O.1CaO.6SiO₂ system, and thusmay be referred to as NCS₆ glass. Unlike conventional soda-lime-silicaglass compositions, the presently disclosed parent glass composition canbe formed into the shape of a glass article and transformed into aglass-ceramic article that exhibits sufficient strength and chemicalresistance for use in packaging a variety of consumer products,including beverages and food. This may be attributed to the ability ofthe parent glass composition to undergo spontaneous homogeneousnucleation, wherein nuclei are formed with equal probability throughouta bulk of the glass, instead of along a pre-existing surface. Inaddition, partial crystallization of the parent glass compositionresults in the formation of a crystalline phase that is enriched insodium (Na), as compared to the parent glass composition and as comparedto the amorphous matrix phase or residual glass phase. Without intendingto be bound by theory, it is believed that trapping a relatively highamount of sodium in the crystalline phase of the glass-ceramic decreasesthe quantity of sodium ions that are susceptible to leaching or releasefrom the glass-ceramic under certain conditions, which improves thechemical resistance of the glass-ceramic.

FIG. 1 illustrates a soda-lime-silica glass-ceramic container 10 havinga soda-lime-silica glass-ceramic body 12, in accordance with oneembodiment of the present disclosure. In the illustrated embodiment, thebody 12, which defines the shape of the container 10, has a longitudinalaxis A. The body 12 provides the container 10 with a closed base 14 atone axial end, a circumferentially closed sidewall 16 extending in anaxial direction from the closed base 14, and an open mouth 18 at anotheraxial end, opposite the base 14. Accordingly, the body 12 is hollow. Inone form, the sidewall 16 may have a thickness, measured from aninterior surface to an exterior surface thereof, in the range of onemillimeter to five millimeters, including all ranges and subrangestherebetween.

The glass-ceramic body 12 is of unitary, one-piece construction andcomprises a soda-lime-silica glass-ceramic material having two phases: acrystalline phase and an amorphous matrix phase. The crystalline phasemay comprise 10 vol % to 70 vol % of the soda-lime-silica glass-ceramicbody 12, with the amorphous matrix phase making up the remaining 30 vol% to 90 vol % of the glass-ceramic body 12, including all ranges andsubranges between these ranges. The “volume percent” or “vol %” of acomponent within a mixture is determined by calculating the volumefraction of the component (by dividing the volume of the component bythe volume of all of the components within the mixture) and multiplyingby 100. In some specific embodiments, the volume fraction of thecrystalline phase in the glass-ceramic body 12 may be greater than orequal to 0.10, 0.20, or 0.30; less than or equal to 0.70, 0.50, or 0.40;or between 0.10-0.70, 0.20-0.50, or 0.30-0.40.

The overall chemical composition of the soda-lime-silica glass-ceramicbody 12, including the crystalline phase and the amorphous matrix phase,may comprise 47-63 mol % SiO₂, 15-22 mol % Na₂O, and 18-36 mol % CaO,including all ranges and subranges between these ranges. The “molepercent” or “mol %” of a component within a mixture is determined bycalculating the mole fraction of the component (by dividing the numberof moles of the component by the number of moles of all of thecomponents within the mixture) and multiplying by 100. In one specificembodiment, the overall chemical composition of the soda-lime-silicaglass-ceramic body 12 may comprise about 50 mol % SiO₂, about 17 mol %Na₂O, and about 33 mol % CaO. As used herein the term “about” meanswithin 1%.

The presently disclosed soda-lime-silica glass-ceramic body 12 has beenfound to exhibit suitable chemical, mechanical, and thermal propertieswithout the addition of Al₂O₃ and/or MgO, which are conventionallyincluded in soda-lime-silica glass compositions to improve chemicalresistance and inhibit the ability of the glass to crystallize. As such,the presently disclosed soda-lime-silica glass-ceramic body 12 may besubstantially free of Al₂O₃ and/or MgO. In one form, soda-lime-silicaglass-ceramic body 12 may include less than 0.9 mol % Al₂O₃ and lessthan 2.2 mol % MgO, and preferably less than 0.6 mol % Al₂O₃ and lessthan 1.0 mol % MgO.

The crystalline phase provides the glass-ceramic body 12 with improvedfracture toughness, as compared to fully amorphous materials havingsimilar chemical compositions, and comprises a plurality of crystallineparticles homogeneously dispersed throughout the amorphous matrix phase.The crystalline particles in the glass-ceramic body 12 comprise solidsolution crystals having a hexagonal crystalline structure substantiallyidentical to that of a stoichiometric Na₂O.2CaO.3SiO₂ composition,commonly referred to as combeite. In one form, the crystalline particlesmay have particle sizes in the range of 0.1 μm to 50 μm, including allranges and subranges therebetween. Unlike the crystalline phases whichtypically form during devitrification of conventional soda-lime-silicaglass compositions, the crystalline phase of the presently disclosedNC₂S₃ glass-ceramic does not include particles of devitrite(Na₂O.3CaO.6SiO₂), wollastonite (CaO.SiO₂), or of a silica (SiO₂)polymorph (i.e., quartz, cristobalite or tridymite).

The crystalline phase of the glass-ceramic body 12 is enriched in sodium(Na) relative to the amorphous matrix phase and relative to astoichiometric Na₂O.2CaO.3SiO₂ composition. This means that, althoughthe structure of the crystalline particles is substantially identical tothat of combeite, the sodium content of the crystalline phase is greaterthan that of a stoichiometric Na₂O.2CaO.3SiO₂ composition and also isgreater than that of the amorphous matrix phase.

In one form, the crystalline phase may comprise 12-17 at % Na and theamorphous matrix phase may comprise 9 at % to 13 at % Na. By comparison,a conventional soda-lime-silica glass composition generally comprises8.3 at % to 9.6 at % Na, or, more specifically, 8.6 at % to 9.3 at % Na.The “atomic percent” or “at %” of one kind of atom within a mixture iscalculated by dividing the number of atoms of that kind by the totalnumber of atoms within the mixture and multiplying by 100. The sodiumcontent of the crystalline phase will depend upon the degree ofcrystallization, with the sodium content decreasing as the volumefraction of the crystalline phase increases until the volume fractionreaches unity.

Referring now to FIG. 2, a method of manufacturing a soda-lime-silicaglass-ceramic article, such as the glass-ceramic container 10illustrated in FIG. 1, includes a melting stage, a forming stage, and athermal treatment stage.

In the melting stage, glass batch materials are melted, for example, ina glass furnace, to produce a thermally crystallizable soda-lime-silicaparent glass composition. The parent glass composition is formulated toapproximate a stoichiometric Na₂O.2CaO.3SiO₂ system and may comprise 47mol % to 63 mol % SiO₂, 15 mol % to 22 mol % Na₂O, and 18 mol % to 36mol % CaO, including all ranges and subranges between these ranges. Insome specific embodiments, the mole fraction of Na₂O in the parent glasscomposition may be greater than or equal to 0.15, 0.16, or 0.165; lessthan or equal to 0.22, 0.19, or 0.17; or between 0.15-0.22, 0.16-0.19,or 0.165-0.17; the mole fraction of CaO in the parent glass compositionmay be greater than or equal to 0.18, 0.30, or 0.32; less than or equalto 0.36, 0.35, or 0.34; or between 0.18-0.36, 0.30-0.35, or 0.325-0.34;and the mole fraction of SiO₂ in the parent glass composition may begreater than or equal to 0.47, 0.48, or 0.49; less than or equal to0.63, 0.53, or 0.51; or between 0.47-0.63, 0.48-0.53, or 0.49-0.51. Inone form, the parent glass composition may comprise about 50 mol % SiO₂,about 17 mol % Na₂O, and about 33 mol % CaO.

The parent glass composition may comprise other materials in relativelysmall amounts, e.g., relatively small amounts of one or more of thefollowing: MgO, K₂O, Fe₂O₃, SO₃, V₂O₅, As₂O₃, TiO₂, carbon, nitrates,flourines, chlorines, or elemental or oxide forms of one or more ofselenium, chromium, manganese, cobalt, nickel, copper, niobium,molybdenum, silver, cadmium, indium, tin, gold, cerium, praseodymium,neodymium, europium, gadolinium, erbium, and uranium, to name but a fewexamples. Such materials may be additives, residual materials fromcullet, and/or impurities typical in the commercial glass manufacturingindustry. The total amount of all other materials in the parent glasscomposition may be less than 5.0 mol %, preferably less than 2.0 mol %,and more preferably less than 1.0 mol %.

The parent glass composition may be substantially free of nucleatingagents, e.g., ZrO₂, TiO₂, and/or P₂O₅, and may include less than 0.3 mol% thereof. Also, the parent glass composition may be substantially freeof Al₂O₃ and/or MgO, and may include less than 0.9 mol % Al₂O₃ and lessthan 2.2 mol % MgO.

During the forming stage, an amount of the parent glass composition isformed into a glass body having a container shape. The forming stage iscarried out at a temperature below a melting point (Tm), but above asoftening point (Ts), of the parent glass composition. The parent glasscomposition has a melting point in the range of 1100° C.-1400° C. and asoftening point in the range of 660° C.-740° C. Compared to conventionalNCS₆ glass, however, the parent NC₂S₃ glass composition has a lowviscosity in the molten state and, consequently, is difficult to shearor otherwise consistently partition into pre-weighted gobs due to itshigh flowability. At 1100° C., for example, the viscosity of NC₂S₃ glassis about 10² poise, while at the same temperature the viscosity of NCS₆glass is about 10⁴ poise. Alternative techniques more amenable toforming low viscosity molten materials into defined shapes may have tobe used instead. Spin casting and injection molding are two such formingtechniques that can be employed to form the parent glass compositioninto a glass body without bulk crystallizing the glass composition.

In a preferred embodiment of the forming stage, the parent glasscomposition is formed into the glass body with a container shape by spincasting. During spin casting, a charge of the parent glass composition,which may be at a temperature in the range of 1050° C.-1100° C., ispoured into a casting mold through an inlet opening at the top of themold. The casting mold is spinning on its axis while the parent glasscomposition charge is being introduced into a container-shaped moldcavity of the casting mold and for a period of time thereafter. Thespinning action of the mold and the associated centrifugal force drivesthe molten parent glass composition outwards and into thecontainer-shaped mold cavity and results in rapid cooling of the glass.Specifically, the parent glass composition is cooled without bulkcrystallizing to a temperature of 900° C., or below, which raises theviscosity of the glass enough that it can hold a container shape. Ofcourse, in other embodiments, the parent glass composition can berapidly cooled without bulk crystallizing through the entirecrystallization zone and ultimately below the softening point of theglass. In either scenario, the glass body is obtained in an amorphousstate despite the initially low viscosity of the parent glasscomposition melt and the overlap of the forming and crystallizationtemperature ranges of NC₂S₃ glass.

After the forming stage, the glass body may be transferred to thethermal treatment stage, which may be carried out in an oven or lehr.The thermal treatment stage may be performed according to apredetermined schedule and may be considered to involve three differentstages: nucleation, crystal growth, and annealing, all of which mayoccur at the same or different times during manufacture of thesoda-lime-silica glass-ceramic article.

During the nucleation stage, the glass body is brought to a temperaturewithin a predetermined temperature range at which nuclei are known toform spontaneously and homogeneously throughout a bulk of the parentglass. This may include cooling the glass body after the forming stageto a temperature below the softening point, but above a glass transitiontemperature (Tg) of the parent glass composition. In other embodiments,where the glass body is cooled to a temperature below the glasstransition temperature of the parent glass after the forming stage, theglass body may need to be re-heated to a temperature above the glasstransition temperature, but below the softening point of the parentglass composition. Thereafter, the glass body may be maintained withinthis temperature range for a sufficient amount of time for bulknucleation to occur throughout the glass body. In one form, the parentglass composition may have a softening point in the range of 660°C.-740° C. and a glass transition temperature in the range of 560°C.-585° C. In such case, homogeneous nucleation may be carried out at atemperature in the range of 525° C.-625° C. for a time between 10minutes and 180 minutes. In one specific example, homogeneous nucleationmay be carried out at a temperature in the range of 580° C.-610° C. fora time between 5 minutes to 30 minutes. The temperature at which thenucleation stage is carried out may be adjusted to coincide with thetemperature at which the nucleation rate of the parent glass compositionreaches a maximum (Tn), i.e., 600° C.

During the crystal growth stage, the nucleated glass body is brought toa temperature within a predetermined temperature range at which crystalgrowth is known to occur on pre-existing nuclei in the parent glass. Asthe crystals grow within the parent glass, the glass body is transformedinto a glass-ceramic body. The crystal growth stage is carried out at atemperature below the softening point, but above the glass transitiontemperature of the parent glass composition, albeit closer to thesoftening point. And, in general, the crystal growth stage will becarried out at a higher temperature than that of the nucleation stage.The temperature at which the crystal growth stage is carried out may beadjusted to coincide with the temperature at which the rate of crystalgrowth within the parent glass composition reaches a maximum (Tc), i.e.,about 720° C. After the glass body is brought to a suitable temperaturefor crystal growth, the glass body is maintained at such temperature orwithin a suitable temperature range for a sufficient amount of time fora desired amount of crystal growth to occur on the pre-existing nucleiin the parent glass. In one form, crystal growth may be carried out at atemperature in the range of 600-750° C. for a time between 10 minutesand 120 minutes. In one specific example, the crystal growth stage maybe carried out at a temperature in the range of 680° C.-730° C. for atime between one minute and 30 minutes.

The temperature and duration of the crystal growth stage may becontrolled or adjusted so that the crystalline phase in the resultingglass-ceramic body reaches a target volume fraction and so that thecrystalline particles reach a desired mean particle size. In general,longer heating times will result in glass-ceramic bodies having a higherdegree of crystallization and larger crystalline particles. Suitableadjustment of the crystal particle size and the degree ofcrystallization may allow for the production of glass-ceramic bodieshaving a range of desired mechanical, optical, chemical, and thermalproperties. For example, a greater volume of crystals leads to moreopacity and a shift in the UV absorption edge of the NC₂S₃ glass-ceramicas well as greater chemical durability. Additionally, a greater volumeof smaller sized crystals, such as crystals having a particle size ofless than 20 μm, can positively influence the strength and fracturetoughness of the NC₂S₃ glass-ceramic by acting as crack deflectors thatdeflect cracks, to the extent they form and propagate, along anon-preferred path.

In some embodiments, nucleation and crystal growth may be performed atsubstantially the same time and at substantially the same temperature.In such case, nucleation and crystal growth may be performed by bringingthe glass body to a temperature within a predetermined temperature rangeat which both homogeneous nucleation and crystal growth are known tooccur in the parent glass, and then maintaining the glass body withinthis temperature range for a sufficient amount of time for a desiredamount of crystal growth to occur. In one form, both nucleation andcrystal growth may be carried out at a temperature in the range of 600°C.-625° C. for a time between 5 minutes and 60 minutes.

After the glass-ceramic body has reached a desired degree ofcrystallization, the glass-ceramic body may be annealed, for example,according to an annealing schedule. This may include gradually loweringthe temperature of the glass-ceramic body from a temperature at or abovethe glass transition temperature of the glass to a temperature below astrain point (Tst) of the glass. In one form, the amorphous matrix phaseor glassy portion of the glass-ceramic body may have an annealing pointin the range of 545° C.-585° C. and a strain point in the range of 520°C.-560° C. In such case, annealing of the glass-ceramic body may becarried out at a temperature in the range of 540° C.-580° C. for a timebetween 5 minutes and 25 minutes. After the glass-ceramic body isannealed, the glass-ceramic body is cooled to room temperature at assufficient rate to prevent thermal cracking.

EXAMPLES

Several soda-lime-silica glass and soda-lime-silica glass-ceramicsamples were prepared in a laboratory and analyzed with respect to theirstructural, chemical, and optical properties.

Example 1

A thermally-crystallizable soda-lime-silica glass having astoichiometric Na₂O.2CaO.3SiO₂ glass composition (NC₂S₃) was prepared bymelting a mixture of soda ash, limestone, and sand in platinum cruciblesin a Deltech furnace at 1450° C. for three hours. Specifically, themixture included 76.26 g of soda ash (Na₂CO₃), 144.04 g limestone(CaCO₃), and 129.7 g sand (SiO₂). Samples of the molten NC₂S₃ glass werecast between steel plates and re-melted for 30 minutes to promotehomogeneity. The glass samples were then poured and re-cast betweensteel plates. Differential scanning calorimetry (DSC) was performed onseveral of the NC₂S₃ glass samples. The DSC data revealed acrystallization peak temperature of 720° C. for the NC₂S₃ glass.

Example 2

Several of the NC₂S₃ glass samples prepared in Example 1 were thermallytreated by being heated at a temperature of 720° C. for 30, 60, 90, or120 minutes to transform the glass samples into glass-ceramics. Theglass-ceramic samples were then cooled to room temperature, either at arate of 3-4° C. per minute or 1-2° C. per minute. The crystalline volumefraction and opacity of the glass-ceramic samples were observed and werefound to increase with increasing heating time. In addition, the slowercooling rate of 1-2° C. per minute was found to produce a higher degreeof crystallization than the faster cooling rate of 3-4° C. per minute. Athermal treatment time of 30 minutes at 720° C. resulted inglass-ceramic samples having a crystalline volume fraction in the rangeof 0.20-0.50.

Referring now to FIG. 3, x-ray diffraction (XRD) was performed on aNC₂S₃ glass-ceramic sample heat treated at 720° C. for 30 minutes andcooled at a rate of 3-4° C. per minute (Sample A) and a NC₂S₃glass-ceramic sample that was heat treated at 720° C. for 30 minutes andcooled at a rate of 1-2° C. per minute (Sample B). Sample A had acrystalline volume fraction in the range of 0.20-0.40 and Sample B had acrystalline volume fraction of greater than 0.80. The x-ray powderdiffraction peak positions (degrees 2θ) and relative intensities ofSample A and Sample B are illustrated in FIG. 3. All diffraction peakpositions of Sample A and Sample B were analyzed using JADE peak fittingsoftware and indicate the presence of a combeite crystal phase(Na₂Ca₂Si₃O₉). No secondary crystal phases were observed in either ofthe Samples.

As shown in FIG. 3, the most pronounced diffraction peak (using a CuK_(α1) source) positions and relative intensities of the combeitecrystal phase are located at the following 2θ: 33.62° (100%), 34.25°(98%), 26.87° (62%), 48.75° (59%), and 23.82° (33). In comparison, XRDdata of devitrified conventional NCS₆ glass would show the presence ofother crystal phases such as devitrite, wollastonite, or a silicapolymore such as cristobalite, none of which were detected in Samples Aand B. To be sure, the three dominant diffraction peak positions ofdevitrite (26.98°, 29.87°, and 28.66°), wollastonite (26.88°, 23.20°,and 25.28°), and crisbobalite (23.64°, 34.24°, and 38.42°) are notpresent in the XRD patterns of FIG. 3.

Scanning electron microscopy (SEM) indicates that the crystallineparticles in the glass-ceramic samples exhibit spherical crystalmorphology (spherical shapes) based on the hexagonal structure ofcombeite.

Example 3

Several of the NC₂S₃ glass-ceramic samples prepared in Example 2 werefractured to reveal a fresh surface from within the bulk sample and thensputter coated with a thin layer of gold. Energy dispersive spectroscopy(EDS) was performed on cross-sections or fracture surfaces of the NC₂S₃glass-ceramic samples. In general, the EDS data revealed a higherconcentration of sodium (Na) in the crystalline phase of theglass-ceramic samples than in the surrounding amorphous matrix phase. Inone particular glass-ceramic sample heated at 720° C. for 30 minutes andhaving approximately 30 vol %-50 vol % crystallinity, EDS data was takenfrom six different points along a fracture surface of the sample, withthree of the points taken from different crystalline particles and theremaining three points taken from the surrounding glass (i.e., theamorphous matrix phase). Based upon the resulting EDS data, thecomposition of each of the six points was calculated, as shown in Table1 below.

TABLE 1 Point O (atom %) Na (atom %) Si (atom %) Ca (atom %) 1 (Glass)56.2 10.1 17.5 16.1 2 (Glass) 56.2 10.4 17.7 15.7 3 (Glass) 56.4 9.917.7 16.0 4 (Glass) 56.3 10.2 17.7 15.8 5 (Glass) 56.3 10.0 17.5 16.2 6(Crystal) 56.0 11.4 17.7 14.9 7 (Crystal) 56.1 11.7 18.0 14.2 8(Crystal) 55.9 11.8 17.6 14.8 9 (Crystal) 55.8 11.3 17.1 15.9 10(Crystal) 55.8 11.4 17.3 15.5

Example 4

Several of the NC₂S₃ glass and glass-ceramic samples prepared inExamples 1 and 2 were ground into particles having particle sizes in therange of 297 μm to 420 μm. The hydrolytic resistance of these NC₂S₃glass and glass-ceramic particles was assessed using the Glass GrainsTest set forth in USP <660>“Containers—Glass,” wherein 10 grams of theglass grains are autoclaved in 50 mL of carbon dioxide-free purifiedwater for 30 minutes at 121° C. The leachable quantity of alkali metalions (e.g., Na⁺) per gram of glass grains was calculated based upon theamount of 0.02M HCl needed to bring the test solutions to neutral pH.

For comparison, the Glass Grains Test was performed on a stoichiometric1Na₂O.1CaO.6SiO₂ glass composition (NCS₆) including 75.33 wt % SiO₂,12.95 wt % Na₂O, and 11.72 wt % CaO, as well as a commercial containerglass composition including 72.49 wt % SiO₂, 13.46 wt % Na₂O, 10.47 wt %CaO, 1.32 wt % Al₂O₃, 1.68 wt % MgO, 0.19 wt % K₂O, and 0.23 wt % SO₃.In addition, the Glass Grains Test was performed on a sample of the samecommercial container glass composition after grains of the glass weresintered and crystallized at 750° C. for 24 hours to produce a partiallycrystalline glass-ceramic.

The results of the Glass Grains Test are set forth in Table 2 below. Theamount of 0.02M HCl required to titrate the test solutions to a neutralpH was then converted to an equivalent mass of Na₂O extracted from thesample grains and reported in μg Na₂O per gram of sample grains, withsmaller values indicative of greater hydrolytic resistance or chemicaldurability.

TABLE 2 Amt. of Equiv. mass 0.02M HCl of Na₂O Moles of consumedextracted titrated Na Volume per gram of from sample per gram of TestFraction Replicate sample grains grains glass No. CompositionCrystallized No. (mL/g) (μg/g) (moles/g) 1 NC₂S₃ None 1 0.94 583 1.88 ×10⁻⁵ 2 NC₂S₃ None 2 0.93 576 1.86 × 10⁻⁵ 3 NC₂S₃ 0.2-0.4 1 0.75 465 1.50× 10⁻⁵ 4 NC₂S₃ 0.2-0.4 2 0.76 471 1.52 × 10⁻⁵ 5 NC₂S₃ >0.8 1 0.58 3591.16 × 10⁻⁵ 6 NC₂S₃ >0.8 2 0.58 359 1.16 × 10⁻⁵ 7 NCS₆ None 1 0.76 4711.52 × 10⁻⁵ 8 NCS₆ None 2 0.75 465 1.50 × 10⁻⁵ 9 Container Glass None 10.62 384 1.24 × 10⁻⁵ 10 Container Glass None 2 0.61 378 1.22 × 10⁻⁵ 11Container Glass 0.2-0.4 1 3.00 1859 6.00 × 10⁻⁵ 12 Container Glass0.2-0.4 2 2.97 1841 5.94 × 10⁻⁵

As shown in Table 2, partially crystallized NC₂S₃ glass-ceramiccompositions exhibit greater chemical resistance than amorphous NC₂S₃glass compositions (Test Nos. 3-6 vs. Test Nos. 1-2). And the chemicalresistance of partially crystallized NC₂S₃ glass-ceramic compositionsincreases with increasing degrees of crystallization (Test Nos. 3-4 vs.Test Nos. 5-6). Notably, an exceptional level of chemical resistance wasobserved in the partially crystallized NC₂S₃ glass-ceramic samples,without addition of Al₂O₃. Also, an amorphous commercial container glasscomposition including 1.3 wt % Al₂O₃ exhibits greater chemicalresistance than an amorphous NCS₆ glass composition that does notinclude Al₂O₃ (Test Nos. 9-10 vs. Test Nos. 7-8). Further, partialcrystallization of a commercial container glass compositionsignificantly reduces the chemical resistance of the composition (TestNos. 9-10 vs. Test Nos. 11-12).

Example 5

The optical properties of several of the NC₂S₃ glass and glass-ceramicsamples prepared in Examples 1 and 2 were analyzed, along with a sampleof a commercial flint container glass composition including 72.49 wt %SiO₂, 13.46 wt % Na₂O, 10.47 wt % CaO, 1.32 wt % Al₂O₃, 1.68 wt % MgO,0.19 wt % K₂O, and 0.23 wt % SO₃. FIG. 4 illustrates plots ofTransmission (%) vs. Wavelength (nm) through the following samples: (1)an amorphous NC₂S₃ glass composition, (2) a NC₂S₃ glass-ceramiccomposition prepared by thermal treatment at 720° C. for 15 minutes, (3)a NC₂S₃ glass-ceramic composition prepared by thermal treatment at 720°C. for 30 minutes, (4) a NC₂S₃ glass-ceramic composition prepared bythermal treatment at 590° C. for 24 hours, (5) a NC₂S₃ glass-ceramiccomposition prepared by thermal treatment at 590° C. for 24 hoursfollowed by 720° C. for 30 minutes, and (6) an amorphous commercialflint container glass composition. Further details of the chemical,structural, and optical properties of these samples are set forth inTable 3 below.

TABLE 3 Volume Crystal Trans. at Trans. at Sample Thermal Fraction Size400 nm 550 nm No. Composition treatment Crystallized (μm) (%) (%)Appearance 1 NC₂S₃ None None None 85.9 89.7 Transparent 2 NC₂S₃ 720° C.,15 min.  <5%  5-15 85.8 88.2 Translucent 3 NC₂S₃ 720° C., 30 min.30-50%  20-50 39.4 51.8 Translucent 4 NC₂S₃ 590° C., 24 hr. 5-10% 1-556.4 66.2 Transparent 5 NC₂S₃ 720° C., 15 min. +  >90%  1-10 0.3 0.4Opaque 590° C., 24 hr. 6 Flint Container None None None 85.4 86.8Transparent

There thus has been disclosed a soda-lime-silica glass-ceramic articleand a method of manufacturing a soda-lime-silica glass-ceramic articlethat fully satisfies one or more of the objects and aims previously setforth. The disclosure has been presented in conjunction with severalillustrative embodiments, and additional modifications and variationshave been discussed. Other modifications and variations readily willsuggest themselves to persons of ordinary skill in the art in view ofthe foregoing discussion. For example, the subject matter of each of theembodiments is hereby incorporated by reference into each of the otherembodiments, for expedience. The disclosure is intended to embrace allsuch modifications and variations as fall within the spirit and broadscope of the appended claims.

The invention claimed is:
 1. A method of manufacturing asoda-lime-silica glass-ceramic container comprising: forming a glassbody from a parent glass composition comprising 47-63 mol % SiO₂, 15-22mol % Na₂O, and 18-36 mol % CaO, the glass body being in the shape of acontainer; and subjecting the glass body to a thermal treatment scheduleto promote bulk in situ crystallization of the glass body such that theglass body is transformed into a glass-ceramic body having an amorphousmatrix phase and a crystalline phase homogeneously dispersed throughoutthe amorphous matrix phase, the crystalline phase comprising combeitecrystalline particles.
 2. The method set forth in claim 1, wherein thethermal treatment schedule comprises: a nucleation stage wherein theglass body is brought to a temperature in a range of 525° C.-625° C. andmaintained within the range of 525° C.-625° C. for 10 minutes to 180minutes such that a plurality of nuclei spontaneously form within theglass body; and a crystal growth stage wherein the glass body is broughtto a temperature in a range of 600° C.-750° C. and maintained within therange of 600° C.-750° C. for 10 minutes to 120 minutes such that aplurality of crystalline particles form on the pre-existing nuclei. 3.The method set forth in claim 1, wherein, during the crystal growthstage, the glass body is maintained at a temperature in a range of 600°C.-750° C. for an amount of time to transform the glass body into aglass-ceramic body having a crystalline volume fraction in the range of0.10 to 0.70.
 4. A method of manufacturing a soda-lime-silicaglass-ceramic container comprising: forming a glass body from a parentglass composition comprising 47-63 mol % SiO₂, 15-22 mol % Na₂O, and18-36 mol % CaO, the glass body being in the shape of a container; andsubjecting the glass body to a thermal treatment schedule to promotebulk in situ crystallization of the glass body such that the glass bodyis transformed into a glass-ceramic body having an amorphous matrixphase and a crystalline phase homogeneously dispersed throughout theamorphous matrix phase, wherein the glass body is not cooled to atemperature below a glass transition temperature of the parent glasscomposition prior to being subjected to the thermal treatment schedule.5. The method set forth in claim 1, wherein the thermal treatmentschedule comprises: a combined nucleation and crystal growth stage,wherein the glass body is brought to a temperature in a range of 600°C.-750° C. and maintained within said range for 10 minutes to 180minutes.
 6. The method set forth in claim 1, wherein the thermaltreatment schedule comprises: an annealing stage, wherein theglass-ceramic body is gradually cooled to a temperature below a strainpoint of the amorphous matrix phase to reduce internal stresses withinthe glass-ceramic body.
 7. A method of manufacturing a soda-lime-silicaglass-ceramic container comprising: forming a glass body from a parentglass composition comprising 47-63 mol % SiO₂, 15-22 mol % Na₂O, and18-36 mol % CaO, the glass body being in the shape of a container;maintaining the glass body at a temperature between 525° C. and 600° C.to form nuclei spontaneously and homogeneously throughout the glassbody; maintaining the glass body at a temperature between 600° C. and750° C. to grow crystals on the nuclei throughout the glass body andthereby transform the glass body into a glass-ceramic body; andannealing the glass-ceramic body at a temperature between 540° C. and580° C. followed by cooling the glass-ceramic body to a temperaturebelow a strain point of the amorphous glass matrix of the glass-ceramicbody to reduce internal stresses within the glass-ceramic body.
 8. Themethod set forth in claim 7, wherein the glass body is not cooled to atemperature below the glass transition temperature of the parent glasscomposition prior to maintaining the glass body at a temperature between525° C. and 600° C. to form nuclei spontaneously and homogeneouslythroughout the glass body.
 9. The method set forth in claim 7, whereinthe glass-ceramic body comprises combeite crystalline particleshomogeneously dispersed within an amorphous glass matrix, and whereinthe glass-ceramic body does not include particles of devitrite(Na₂O.3CaO.6SiO₂), wollastonite (CaO.SiO₂), or a SiO₂ polymorph.
 10. Themethod set forth in claim 7, wherein the glass body is maintained at atemperature between 580° C. and 610° C. to form nuclei, and wherein theglass body is further maintained at a temperature between 680° C. and730° C. to grow crystals on the nuclei.